Electrode for high-frequency heating of insulation preforms



June 7, 1949. D ND 2,472,370

ELECTRODE FOR HIGH-FREQUENCY HEATING OF INSULATION PREFORMS Filed Jan.8, 1945 SOURCE OF HIGH FREQUENCY CURRENT.

SOURCE OF 7 HIGH FREQUENCY 4,

CURRENT.

Patented June 7, 1949 EnncTRoDE FOR HIGH-FREQUENCY HEAT- INGOF=INSULATIONTREFOBMS has en Di ru ma d ke W a siego t Gu e -Hammen. InM lw ukee W S-l a c otnoliation of Delaware ApplicationlJanuary 8, 1945;Serial: No. $71,778

3,. Claims.

This invention relates, to improvements. in electrode a r ieh q e y-he ie o cy i ers, of; i bstan alln co stan l emeter compose of dieleett a me ial. n re part ar iq eatins: herm p s c: nd; os i ne m nee u uc i rm-AL; primary, object of: the invention is to provide cooperating; highfrequency electrodes. ada ed; toms s bs an ia l o m a i o he entire o n:n ula f or srnuplqf nre nrm o c ind ic l orskm- Arnothenobject is toprovide a nor-mallystationary; eleot node off such lform= as ;toinsureproper p ition n of-= ns lat o nrsi l o l n ri on l s rs ape wh nosi d e sen n t ser la nnshin h e Anqther -an-d more specific objectisto provide a trough-shaped; supporting electrode which. not n nstabize -:1 the. c dr c d skr hap nrei-ormswhem seated-fids w se h reresverse; relationship thereto butalso serves to im-. prove currentdistribution through; such prefoprns; thus overcoming: the mechanicaland-electrical; disadvant es lfi t l t e h used for such purpose.

Another ohiect isetolprovidelfor use ore-an upper electrode Q i ithtnverte r u h-s e r, offlat; o m; w heut; sacri i n f: the a r tagesattendant upon use; of: a. troug-h shaped; we :ot' upportinaele ro e;

Anothcn object isto provide.- f or use of cornnlementar-yl. ever ar anes l tr des: so veni a e o ae e m a e h eb we nl reterm r f r s Qtirsula or n ransverse ess s i n he b eid-ele t es i t; v: s r oun lati ea e tipn 0ft t ne phera iar goirthe e o msi w th o s qu ntsubstantiallmuniform heatingof; all portions of: eeh ierm- Qthertqbiects and; adantag s of en on ih reinaiter, nn

The nanyiee it w nes lustr te certain embodiments of theinventio n whichwill now be described; it. being understood. that the invention is.susceptible oi embodiment, in other. forms without. departing from. thescope vof the apte desi ims- In the drawings, Eigure 1;, is, asideelevational, iewlot a pa r iu er andlpw rhi hi t uency, electrodes.ofapprojiimately. semi-circular form in transverse cross section toaccommodate h rsh we n. n mor p e ences, o rdi ctr o ma er al; Q eim leewer in t a sv s a s; seamen-l he. we -electrode s vinaraselst biliz:msupmstige he prsisz ms.

Fig. 2,; is a sectional view on the line 2--2 of Fig. 3 illustrates amodified form of my invention wherein theupper electrode is of the usualflatf-orm, and the lower or supporting electrode isvin the: form ofatrough; the same com.- prising a pairot longitudinally straight, flatsidesconverging at;arelatively Wide angle toward each ither-land Eigsiisa sectional view on the line 4-4 of In the'art; oitransfer-molding ofthermoplastic or' thermosetting insulating materials, of the Bakelitetype for instance; it has heretofore been proposed gto pmvide preformedslugs or disks ofsuch material; and toheat such slugs between a, pair ofhigh igtequency electrodes to render the sarn e qf; the desired degreeof plasticity for use in the molding; machine; especially Where atransfer molding-machine is employed.

In practice suchpref-orms are generally in the form; ofr ound disks orcylinders; because that isthe most convenient form of the pieces for usein themolding machines; and also because the die cavities; forpreform-ing suchtablets are most economically made in that shape. Theuseo-i a pair of flat; hig-hfrequency electrodes heretofore usedfor;heating and plasticizingsuch preforms has :not been satisfactorytasiswellknownby those skilled in this art, although there is nodifficulty in insuring a o onstant unlike-diameter of all of suchdiskshaped prefiorms, there isaninherent likelihood. that suchrpreforrns will difier from each other in thickness. on axial length.Therefore, even though a plurality of: such disk-shaped preforms are.placed} individually upon a fiat lower sup porting electrode there willlikely be substantial difienence, in the; distances between the upper.ends thereof and an upper electrode of the flat type. When such.preformsare placed end, to end flatvvise in groups of two or more, toform p les, eat d fletwis p n t at pport ng electrode the aforementionedcondition may be considerably aggravated. That is to say, there may berelatively wide difierences in the air gaps between the tops oftheseveral piles of preforms and the flat upper electrode, with resultantuneven or'-unequal heating-- of the preforms in the various piles.Moreover, the operation of so arrangingtthe-lpreforms inpilesupon thefiat lower or supporting. electrode was time consuming, and

the. operation of gathering: the piles of heated slugs from. such. Swm-ting electrode. and droppingtheniainto theiwellzof thetransferl-moldng:

machine was likewise slow; whereas speed of operation in such a systemis very desirable to provide for attainment of the best results.

As aforeindicated, although there are inherent differences in theheights of the preforms, due to the differences in the amounts ofmaterial em bodying the same, variations in molding pressure, presenceof molding fins, etc., such preforms will all be of like diameter, and Iaccordingly utilize this physical characteristic of such preforms toadvantage.

As shown in Figs. 1 and 2 the lower or supporting electrode iii,composed of a suitable metal is of approximately semicircular form intransverse cross section, the same preferably having curved ordownwardly curled edges ii and H2 at opposite longitudinal sidesthereof. The upper electrode 63 of like metal may be of exactly the sameand dimensions as the electrode and is arranged in reverse relationshipto the latter so as to be complementary thereto for receptionthereloetween of a group of cylindrical preforms arranged end to endrelationship, or with their flat ends adjacent to or contacting witheach other. The upwardly extending curled or curved edges of electrode53 are designated by numerals H3 and 55, respectively.

Also as indicated in Figs. 1 and 2 the troughshaped lower electrode i ispreferably arranged lengthwise in a horizontal plane, to facilitatedepositing of the insulation preforms is thereinto, either singly or ina cylindrical group. Said preforms when so deposited within thetroughshaped electrode Iii are mechanically stabilized in a centralposition transversely thereof, as best illustrated in Fig. 2; the samebeing seated against the central. portion of the trough, and beingspaced 2. gradually increasing distance from the trough on oppositesides of the center of the latter. The upper electrode is is preferablymovable upwardly, or upwardly and laterally, a sufficient distance tofacilitate depositing of the preforms within electrode i0, eithermanually or otherwise. Thereafter electrode I3 is lowered to apredetermined operative position, usually in contact with the preform orpreforms, as shown in Figs. 1 and 2. By this means high frequencycurrent is supplied and penetrates the preforms i B in a large number ofpaths extending substantially throughout the periphery thereof,

as indicated by the imaginary dotted lines I! and H3 in Fig. 2. As aconsequence, substantially the entire transverse or cross sectional areaof the preforms will be subjected to a like heating effect of the highfrequency current supplied to electrodes ill and it, as indicateddiagrammatically at 99 in Fig. 1; it being understood that electrodesll] and i3 act as the plates of a condenser, so that with thearrangement illustrated substantially uniform heating of the entire massof the preforms is insured. In practice care is exercised to insure thatthe adjacent pairs of curved edges ll, i5 and 52, i l of electrodes itand i3 are maintained spaced from each other a sufficient distance toavoid any possibility of arcing between the electrodes orshort-circuiting thereof around the preforms.

After the preforms i6 have thus been subjected to a predetermineddesired or required amount of heat treatment, the supply of highfrequency current is interrupted in any suitable manner, whereupon theupper electrode is is'preferably raised to permit ready and speedyremoval of the preforms, either manual or otherwise, for

feeding thereof into the well of a transfer molding machine or the like(not shown).

In the modification illustrated in Figs. 3 and 4, the lower orsupporting electrode 20 is also of trough-shape in transverse crosssection; the same having a pair of longitudinally extending straight,flat portions arranged at an obtuse angle to each other, as bestillustrated in Fig. 4. This form of supporting electrode is mechanicallyequivalent to the electrode in aforedescribed, in respect of centeringand stabilization of the insulation preforms i it. Also as indicated indotted lines at El in Fig. 4, imaginary paths 2| of the high frequencycurrent from electrode 20 to the preforms it are electrically andfunctionally quite similar to those indicated at I8 in Fig. 2.

The upper electrode 22 in Figs. 3 and 4 may be of the usual flat form,as shown; the same c0- operating with electrode 20, in respect of thepreforms it, to afford substantially complete and equalized heating ofthe entire cross sectional area of the preforms. In practice suchcooperation involves proper spacing of the upper electrode 22 from thepreforms to insure the uniform heating afo "mentioned. The most closelyadjacent portions of electrodes ill and 722 are maintained separated asuflicient distance for reasons set forth in connection with Figs. 1 and2. The edges of upper electrode 22 are preferably bent upwardly, and theedges of lower electrode 20 are bent downwardly, as shown, to assist ininsuring against arcing therebetween. Electrodes 20 and 22 may besupplied with high frequency current from a suitable source it, asaforedescribed.

The upper electrode 22 is movable, as described in connection with thedevice of Figs. 1 and 2, to facilitate insertion of the preforms intoand removal thereof from the electrode 20.

The stationary lower electrodes in and 20 in the respective devices arepreferably attached to suitable supporting members, fragments of whichare shown at 23 and 2 3 whereas the respective upper electrodes areprovided with adjustable supporting and lifting means, fragments ofwhich are shown at 25 and 26.

Although, as illustrated herein, I prefer to pro vide for horizontalpositioning of the pairs of electrodes iii, i3 and 2E], 22 to facilitatedepositing of the preforms, supporting the same for heat treatment, andthereafter removing the same; it is to be understood that certainelectrical and/or functional advantages of my invention may be obtainedby vertical mounting of the pairs of electrodes. This is especially truewith respect to vertical mounting of the semicircular electrodes it andit of Figs. 1 and 2; in which case the vertical charge or pile ofpreforms might be separately supported in exactly centered relationshipto both electrodes of the pair. Such centering of the preforms might beconveniently provided by positioning the same within a tube of suitableglass or ceramic composition.

I claim:

1. In combination, a trough-shaped sheet metal electrode for use in highfrequency heating of cylindrical preforms of thermosetting dielectricmolding material, means for mounting said electrode horizontally withthe trough thereof opening upwardly whereby the same is adapted to actdirect y a centering support for the preforms, the side edges of saidelectrode being equally spaced throughout the length thereof a distancegreater than the diameter of the preforms to effect substantialequalization of the heating effect upon the latter of'high frequencycurrent passed between the same and said electrode, a second electrodeoverlying the horizontal supporting trough formed by said firstelectrode throughout the length of the latter, and the longitudinaledges of said last mentioned electrode being alined with and spaced fromthose of the first mentioned electrode a sufiicient distance to avoidany possibility of arcing between the electrodes or short-circuitingthereof around the preforms.

2. In combination, a pair of like trough-shaped sheet metal electrodesfor use in high frequency heating of cylindrical preforms ofthermosetting dielectric molding material, said electrodes being ofapproximately semicircular form in transverse cross section, means formounting one of said electrodes with the open side thereof facingupwardly in a horizontal plane to form a directly supporting receptacle,means for mounting the other electrode in overlying relationship to thefirst electrode, to complementally accommodate therebetween a pluralityof the cylindrical preforms arranged in end to end relationship, thelongitudinal edges of each electrode being spaced apart a distancesubstantially greater than the diameter of the preforms, said edges ofthe respective electrodes being alined with each other and spaced aparta sufficient distance to avoid any possibility of arcing between theelectrodes when in use, and associated means for effecting movement ofat least one of said electrodes with respect to the other.

3. In combination, a trough-shaped sheet metal electrode for use in highfrequency heating of cylindrical preforms of thermosetting dielectricmolding material, means for mounting said electrode horizontally withthe trough thereof opening upwardly to form a supporting receptacle, theside edges of said electrode being equally spaced throughout the lengththereof a distance greater than the diameter of the preforms to effectsubstantial equalization of the heating ef- 6 feet upon the latter ofhigh frequency current passed between the same and said electrode, asecond electrode overlying the horizontal trough formed by said firstelectrode throughout the length of the latter, the longitudinal edges ofsaid electrodes being vertically alined with each other, thelongitudinal edges of said second mentioned electrode being spaced fromthose of the first mentioned electrode a sufiicient distance to avoidany possibility of arcing between the electrodes or short-circuitingthereof around the preforms, atleast one of said electrodes beingmovable with respect to the other, said first mentioned electrode beingof a relatively wide V-shape in transverse cross section, and saidsecond mentioned electrode being fiat.

LESTER D. DRUGMAND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,179,261 Keller Nov. 7, 19392,231,457 Stephen Feb. 11, 1941 2,288,268 Crandell June 30, 19422,303,983 Brown Dec. 1, 1942 2,304,958 Rouy Dec. 15, 1942 2,306,105Grave et al Dec. 22, 1942 2,347,324 Johnson Apr. 25, 1944 2,390,572DeBrabander Dec. 11, 1945 2,396,004 Gilbert Mar. 5, 1946 OTHERREFERENCES Timbi and Bush Principles of Electrical Engineering, page481, published 1923.

Journal of Applied Physics, Oct. 1943, page 546, vol. 14, No. 10.

Electronics, March 1944, page 230.

Modern Plastics, June 1944, page 111.

